In the recombinant screening program during the past year, we screened approximately 5,000 mice for crossing over, mutation, and genetic variation. We picked up 10 new recombinants. The recombinants are being established as congenic inbred strains before further analysis will be carried out. Two recombinants from the previous year were established as congenic strains and made available to laboratories outside. We extended our studies in gene complementations to show all the possible allelic combinations which can generate new I region gene products capable of antigen presentation. By using an Ia mutant, we were unable to show that Ir genes, MLR determinants, and Ia antigens are coded by the same gene. In the past year, we have also shown that Ia molecules mediate autoimmunity in the case of myasthenia gravis. We have established a model for rheumatoid arthritis in mice and have mapped the genes involved with the I region. Further studies are also currently underway on the genetics of parasite infection, and thyroiditis. We have also found that the immune response to an oligospecific molecule such as hemoglobin could be directed against different determinants on different chains. Some of it might signal a negative effect inducing suppression.